It is known to be desirable to protect enzymes and components having compatibility problems with other components in liquid detergent concentrates. There have been many proposals in the literature to protect the enzyme from the continuous phase of the concentrate and/or water by providing a continuous shell and/or a matrix which is intended to protect the enzyme from the concentrate but to release it when the detergent concentrate is added to water to provide wash water. Examples are given in EP 356,239 and WO 92/20771, and the prior art discussed in those. These, and other known methods, generally involve forming the shell by coacervation.
Unfortunately it is very difficult to select a coacervation polymer and its conditions of use on the one hand, and a polymeric or other core composition on the other, so as to obtain in particles of high specific area the optimum protection and release performance that is required. In general, either the shell is too impermeable to give effective release when required or the shell permits premature release.
Various encapsulation techniques other than coacervation are known for various purposes and one such technique which has been used for other processes is inter facial condensation (IFC) polymerization. IFC encapsulation techniques are generally conducted in oil-in-water dispersions (so that the oil phase becomes the core) but it is also known to conduct IFC encapsulation on a water-in-oil dispersion (so that the water phase becomes the core).
Grunwald et al. “Nylon polyethyleneimine microcapsules for immobilizing multienzymes with soluble dextran-NAD+ for the continuous recycling of the microencapsulated dextran-NAD+”, Biochem and Biophys Res Comm, vol. 81, 2 (1978), pp. 565-570, discloses preparation of semipermeable nylon polyethyleneimine microcapsules containing a multi-enzyme system of yeast alcohol dehydrogenase (EC 1.1.1.1) and malic dehydrogenase (EC 1.1.1.37) together with a soluble immobilized coenzyme, dextran-NAD+.
Poncelet et al. “Microencapsulation within crosslinked polyetyleneimine membranes”, J. Microencapsulation, vol. 11, 1 (1994), pp. 31-40, discloses a microencapsulation technique involving formation of a PEI membrane, which is particularly suited for immobilization of biocatalysts.
WO 97/24177 describes a liquid detergent concentrate with enzyme containing particles. The particles have a polymer shell formed from a condensation polymer, and contain a core polymer which causes stretching of the polymer shell upon dilution of the detergent concentrate in water. Encapsulated precipitated enzymes are also disclosed.
JP-A-63-137996 describes liquid detergents containing encapsulated materials wherein the encapsulation can be by coacervation or by IFC polymerization. The objective in JP 63-137996 is to include in the core a water-soluble or water absorbent polymer that will swell sufficiently when the detergent is put into wash water to cause rupture of the capsules, with consequential release of the core.
We have found that it is not possible to achieve the desired result using any of the microencapsulation procedures previously described for encapsulating enzymes and components having compatibility problems with other components in liquid detergent concentrates. In practice, either the membrane is generally too permeable to prevent migration of the relatively low molecular weight enzyme through the high specific surface area provided by the membrane, or the membrane is so impermeable and strong that it cannot reliably release the enzyme when the concentrate is added to wash water. The processes are not capable of easy reproducible operation to give the desired combination of properties.
The prior art references have failed to acknowledge the usefulness of microcapsules based on polybranched polyamines, such as PEI, for improving the storage stability of enzymes and other components in detergents, while at the same time being capable of delivering the content of the microcapsule timely in a detergent application.